This invention relates to a polished-piece holder, and more particularly to a holder for holding a piece to be polished (xe2x80x9chereinafter referred to as xe2x80x9cpolished piecexe2x80x9d) such as a silicon wafer, a hard disc or the like.
Manufacturing of a silicon wafer, a hard disc or the like includes a step of polishing a surface thereof into a plane or flat shape. During the polishing step, a polished piece such as a silicon wafer, a hard disc or the like is held on a polished-piece holder called a wafer carrier or a disc carrier for plane polishing.
In general, a polished-piece holder is formed into a disc-like shape while being formed on an outer periphery thereof with a gear and is provided with at least one through-hole in which a polished piece is supportedly fitted. Polishing of the polished piece held in the polished-piece holder is carried out by arranging the polished-piece holder in a polishing apparatus so that the gear formed on the outer periphery thereof may be engaged with an internal gear and a sun gear of the polishing apparatus. Then, the sun gear of the polishing apparatus is rotated to cause planetary motion of the polished-piece holder. This permits a polishing cloth to polish a surface of the polished piece into a plane shape.
Conventionally the polished-piece holder is constructed of a laminate formed by laminating a plurality of prepregs on each other and heating the laminated prepregs while applying a pressure thereto in a direction of lamination thereof. The prepregs each are made by impregnating a sheet-like fibrous substrate with thermosetting resin, followed by drying of the, substrate. Such a laminate is generally used for electrical insulation. The laminates include a cotton cloth-phenolic resin laminate formed by laminating a plurality of prepregs each made by impregnating a fibrous substrate of a cotton cloth with phenolic resin on each other, a glass fiber woven fabric substrate-epoxy resin laminate formed by laminating a plurality of prepregs each made by impregnating a fibrous substrate of a glass fiber woven fabric with epoxy resin on each other, a glass fiber nonwoven fabric substrate-epoxy resin laminate formed by laminating a plurality of prepregs each made by impregnating a fibrous substrate of a glass fiber nonwoven fabric with epoxy resin on each other, a laminate formed by laminating a plurality of prepregs each made by a fibrous substrate of a glass fiber woven fabric with epoxy resin and a plurality of prepregs each made by impregnating a fibrous substrate of a glass fiber non-woven fabric with epoxy resin on each other, and the like. Of the laminates, the cotton cloth-phenolic resin laminate and glass fiber woven fabric substrate-epoxy resin laminate are typically used for the polished-piece holder.
Another polished-piece holder is disclosed in Japanese Patent Application Laid-Open Publication No. 304859/1994, which includes a core layer constituted of a prepreg made by impregnating a fibrous substrate of polyester with thermosetting resin such as epoxy resin or the like. Then, the core layer is formed on each of both surfaces thereof with a surface layer, which is constituted of a prepreg made by impregnating a glass fiber substrate with thermosetting resin. Also, the publication discloses a polished-piece holder having a core layer made of polyurethane resin.
Japanese Patent Application Laid-Open Publication No. 254026/1997 discloses a polished-piece holder of which at least an outer periphery is formed of a glass fiber substrate-epoxy resin laminate, a carbon fiber substrate-epoxy resin laminate or an aramid fiber substrate-resin laminate, to thereby enhance durability of a gear formed on the outer periphery. Unfortunately, the publication is silent concerning a structure of each of the laminates. Judging from the disclosure of the publication, the laminates each are supposed to be used for electrical insulation. In general, a laminate for electrical insulation does not substantially regard wear resistance as important, as compared with that for a polished-piece holder. Thus, the laminate for electrical insulation disclosed includes a surface layer made of a woven fabric substrate.
In general, a polished-piece holder is highly required to exhibit increased wear resistance, thickness accuracy, warpage resistance and dimensional stability. Also, it is recently required to exhibit increased quality and performance. In particular, it is required to exhibit properties of keeping a polished piece from taking deep scratches. Unfortunately, a laminate used for the conventional polished-piece holder fails to exhibit properties of preventing a polished piece from taking deep scratches, because it is inherently used for electrical insulation rather than holding of a polished piece.
The present invention has been made in view of the foregoing disadvantages of the prior art.
It is an object of the present invention to provide a polished-piece holder which is capable of exhibiting increased wear resistance, thickness accuracy and warpage resistance and preventing a deterioration in polishing accuracy while preventing a polished piece from taking deep scratches.
A polished-piece holder of the present invention includes a thermosetting resin impregnated fibrous layer constituting a surface layer thereof. The thermosetting resin impregnated fibrous layer is provided by subjecting a prepreg made by impregnating a nonwoven aramid fiber substrate with thermosetting resin to heating and pressurizing. More particularly, it is constructed into a laminated structure which includes a core layer and a wear resistant surface layer laminated on at least one of front and rear surfaces of the core layer. In the present invention, the thermosetting resin impregnated fibrous layer constitutes the surface layer and is formed by subjecting a prepreg made by impregnating the nonwoven aramid fiber substrate with thermosetting resin to heating and pressurizing. Aramid fiber is organic fiber increased in tensile strength as compared with common fiber such as cotton, glass fiber or the like. Also, aramid fiber is reduced in hardness, to thereby be soft as compared with inorganic fiber such as glass fiber. Thus, even when polishing operation is carried out on a polished piece while keeping aramid fiber accidentally or unexpectedly adhered to a surface of the piece, aramid fiber keeps the polished piece from taking deep scratches, to thereby prevent it from being defective. In particular, use of a nonwoven fibrous substrate as the aramid fiber substrate as in the polished-piece holder reduces directionality of a variation in dimensions of the polished-piece holder when it is swollen. A woven fabric is different in strength between a warp direction thereof and a weft direction thereof, to thereby be increased in directionality of a dimensional variation thereof. Also, use of a nonwoven fibrous substrate as the aramid fiber substrate prevents a weaving pattern from appearing on a surface of the polished-piece holder when it is warn. Appearance of a weaving pattern on the surface of the polished-piece holder causes an increase in surface roughness of the polished-piece holder, to thereby render flowing of a slurry of a polishing agent nonuniform, leading to a deterioration in polishing accuracy. On the contrary, use of a nonwoven aramid fiber substrate prevents a weaving pattern of the fibrous substrate from appearing on the surface of the polished-piece holder, to thereby keep surface roughness of the polished-piece holder from being increased, even when the fibrous substrate partially appears on the surface of the polished-piece holder due to wearing of the surface of the holder. This keeps flowing of a slurry of a polishing agent from being nonuniform, to thereby eliminate a deterioration in polishing accuracy of the polished-piece holder.
The thermosetting resins impregnated in the aramid fiber substrate may include phenolic resin, epoxy resin, polyester, polyimide and the like. Thermosetting resin relatively increased in heat resistance such as phenolic resin or polyimide which has a moiety such as a benzene nucleus or the like which does not contribute directly to bonding incorporated at a high density in a molecular skeleton thereof is relatively decreased in bonding or adhesive properties although it is hard, so that it tends to generate peeling between the aramid fibrous substrate and the resin or breakage and wearing of the resin during polishing operation. Thus, epoxy resin is preferably used as the thermosetting resin. In order to minimize fragility or brittleness of the epoxy resin, a flexibility providing agent such as rubber is preferably added to the epoxy resin to modify it, resulting in providing flexible epoxy resin which exhibits flexibility after curing as well.
The aramid fibers includes para-aramid fiber and meta-aramid fiber. Para-aramid fiber is increased in mechanical properties such as tensile strength and modulus, to thereby restrain wearing of the polished-piece holder, leading to an increase in durability thereof, as compared with meta-aramid fiber. Also, para-aramid fiber is reduced in moisture absorption as compared with meta-aramid fiber, to thereby be suitable for use in a moist environment. Thus, it is preferable that the aramid fiber substrate is mainly constructed of para-aramid fiber. Para-aramid fibers include poly-p-phenylene terephthalamide fiber and poly-p-phenylene diphenyl ether terephthalamide fiber, both of which may be commercially available.
A content of para-aramid fiber in the polished-piece holder is preferably 17% by weight or more, because it increases strength of the polished-piece holder, to thereby restrain wearing of a gear section thereof, leading to an increase in durability of the polished-piece holder.
The core layer may be constructed into any desired structure. Nevertheless, formation of at least one thermosetting resin impregnated layer into the core layer permits the polished-piece holder to be readily manufactured using an installation for manufacturing a laminate for electrical insulation. Also, construction of at least one thermosetting resin impregnated fibrous layer into the core layer permits the number of layers to be determined or selected as desired, to thereby be readily accommodated to a desired thickness of a polished piece such as a silicon wafer, a hard disc or the like. The thermosetting resin impregnated fibrous layer for the core layer may be formed of either a prepreg made by impregnating a glass fiber substrate in the form of a woven fabric with thermosetting resin or a prepreg made by impregnating a polyester fiber substrate with thermosetting resin. In particular, when the thermosetting resin impregnated fiber layer for the core layer is formed of the prepreg made by impregnating the polyester fiber substrate with thermosetting resin, the polished-piece holder is substantially decreased in warpage as compared with that made of any other fibrous substrate. In particular, use of the polyester fiber substrate in the form of a woven fabric therefor significantly enhances the advantage. Also, formation of the prepreg made by impregnating the polyester fiber substrate with thermosetting resin into the thermosetting resin impregnated fibrous layer for the core layer minimizes occurrence of deep scratches on a polished piece, as compared with formation of the prepreg made by impregnating the glass fiber substrate in the form of a woven fabric with thermosetting resin into the core layer. This would be for the reason that the glass fibers are harder than the polyester fibers.